Noncaking photographic acid fixing powders



Patented Apr. 8, 1952 UNITED STATES PATENT crimes 1 NONCAKING PHOTOGRAPHIC ACID FIXING POWDERS;

Edwin s. Wiitala and Donald J. Kridel, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a. corporation of New Jersey No Drawing. Application February 9, 1951,

Serial No. 210,283

9 Claims. 1

This invention relates to photographicfixing powders, and more particularly to an improved single-powder acid fixing powder composition which has substantially no tendency to cake while in a package and exposed to various atmospheric conditions.

Fixing compositions in powder form containing in addition to sodium thiosulfate, commonly called hypo, other substances such as salts of acetic acid, alum, etc., have been known for many years. Fixing solutions which are made by adding water to such powder compositions perform several functions in addition to fixing out the unexposed silver salts of the photographicemulsion. The acid in them neutralizes the developer carried over by films or prints and prevents the fixing bath from becoming alkaline. A hardening agent is often included in such formulas to harden the emulsion and protect it from mechanical injury during subsequent processing or from the slightly elevated temperature employed in drying. Sulfurization inhibitors are also added to prevent interaction between the acids and the thiosulfate. The hardening agent most commonly employed is alum i. e. potassium aluminum sulfate or ammonium aluminum sulfate. Many fixing powders of the acid hardening type "in addition to hypo contain potassium alum as parallels the actual conditions under which the bath 'is employed. The type of curve obtained with the usual fixing bath is one which quickly rises to a maximum and then rapidly falls as more developer is added. When a moderate amount of developer has been added the fixing bath will no I ,longer harden satisfactorily.

or more of the other properties is 'sacrificedto some extent. Thus, for example, it is possible that if an attempt is made to secure the maximum degree of hardening, the rate of sulfurization or of sludging may be adversely affected. Consequently there are several features in present fixing compositions which should be bettered and the instant invention describes such an improvement.

Hardening life is defined as the amount of fixing which can be done during which the fixing bath retains a satisfactory degree of hardening. Hardening life may be measured by plotting the temperature at which the gelatin film begins to melt against the amount of a developer which has been added to the fixing bath. This closely stead of sodium acetate.

' hardening life.

In Patent 1,930,140 of October 10, 1933, a successful method of increasing the hardening life of .a. fixing bath without adversely affecting any of its other qualities is described. Fixing baths made in accordance with the procedure of Patent 1,930,140 will maintain satisfactorily hardening over a much wider range, in other words,- they will still harden satisfactorily "When a large amount of developer has been added to them.

As described in the patent, the acid fixing powders contain a substance capable of furnish-' ing acid components to the bath, such as an alkali metal acetate and boric acid. Satisfactory substances which furnish the acetate ion are sodium acetate and sodium diacetate though other acetates may be employed. Sodium citrate and sodium tartrate may also be employed in- The boric acid is added either as such or is supplied by borax and acetic acid in solution. A small amount of boric acid is, therefore, present in the fixing bath simultaneously with the acetate ion. Alum is also present in the bath composition.

These fixing baths will give a greatly increased They will still harden satisfactorily when from three to four times as much developer is carried over as will render an ordinary bath unfit for futher use.

While these fixing baths operate very satisfactorily. the powders, to which water is added to make up the bath, are-sold in a packaged form These-powders, per se, introduce another difficulty in the problem of obtaining effective fixing operations. I

It 'was found at elevated temperatures e. F. and above that the powders made inaccordance with Patent 1,930,140 tended to cake together and hence cause diificulty in removing a desired amount from the package.-

This caking appears to be a result of moisture liberation from the alum and other powders at such elevated temperatures. On cooling, the liberated moisture is in sufficient amount to cause in which they are quite uniformly mixed together.

fusion of the powder, possibly as hydrates of the hypo.

proved hardening characteristics as comparedto those disclosed in the prior art.

amounts up to 20 grams per liter.

3 Another object of the invention is to provide an acid fixing powder having improved hardening characteristics without the tendency of caking at elevated temperatures.

In accordance with the invention these and other objects are attained by replacing boric acid.

in the acid fixing powders with boric anhydride. The boric anhydride may contain up to 15.0% by weight of free moisture and still be usable in our improved fixing bath. Our studies have indicated that boric anhydride has an advantageous desiccating action and also has the desirable property of remaining as a dry powder upon reacting with the amount of moisture present in the acid fixing powders, that moisture heretofore being the cause of caking. We have discovered that boric anhydride can be substituted in corrected amount of the boric acid in acid fixing powders, as mentioned above, without any apparent disadvantages. This substitution has the great advantage of virtually eliminating the caking of the fixing powder. When these powders are put in a water solution, the boric anhydride forms boric acid in the desired amount.

In these formulas a portion or all of the sodium acetate may be replaced by equivalent amounts of sodium citrate or sodium tartrate acids. However, sodium acetate is preferred. The compositions in Examples 1 and 2 are put in solution in water to make up one liter of fixing bath. These fixing baths will give a greatly increased hardening life. Theyiwill still harden satisfactorily when from three to four times as much developer is carried over as will render many acid fixing baths unfit for further use.

The preferred range of concentration of the acetate ions is from 10 grams per liter to 40 grams per'liter, and the amount of hardeners is not less than 5 grams and is preferably less than 30 grams per liter. Boric anhydride may be present in Only 56.3% of the boric acid content normally present in such baths is requited as boric anhydride, due to the higher borate content in the anhydride.

Comparative test A sample of acid fixing powder of the present invention shown in Example 2 and containing sodium acetate. After one day at 110 F. the acid fixing powder containing boric acid had caked considerably, while the boric anhydride acid fix was perfectly free flowing. After one week at 110 F. the regular fixer was moderately caked and the other with the boric anhydride was free flowing. The solution rate of the boric anhydride fixer sample was comparable to the regular, if not better. It can be considered better in that no slowly soluble lumps are introduced into the solution as is the case with a caked material.

Our invention, therefore, supplies to the art a valuable improvement in the fixing powder field.

What we claim and desire to secure by Letters Patent of the United States of America is:

1. A non-caking acid fixing powder composition containing sodium thiosulfate, an alkali sulfite, a hardening agent, boric anhydride, and a salt of-a solid organic acid selected from the group consisting of acetic, citric and tartaric acids.

2. A noncaking acid fixing powder composition containing sodium thiosulfate, an alkali bisulfite, a hardening agent, boric anhydride, and a salt of a solid organic acid selected from the group consisting of acetic, citric and tartaric acids.

3. A non-caking acid fixing powder composition containing sodium thiosulfate, an alkali sulfite, a hardening agent, boric anhydride, and an alkali metal acetate.

4. A non-caking acid fixing powder composition containing sodium thiosulfate, sodium sulfite, alum, boric anhydride and sodium acetate.

5. A non-caking acid fixing powder composition containing sodium thiosulfate, sodium sulfite, alum, boric anhydride and sodium citrate.

'6. A substantially non-caking powdered material capable, when dissolved, of constituting an acid hardening fixing bath comprising:

Grams Anhydrous sodium thiosulfate Sodium sulfite 5 Sodium bisulfite 5 Boric anhydride 2.8 Sodium acetate 22.5 Ammonium alum 22.5

7. A substantially non-caking powdered material capable, when dissolved, of constituting an acid hardening fixing bath comprising I Grams Anhydrous sodium thiosulfate 300 Sodium bisulfite 12.5 Potassium alum 15.0 Sodium acetate 18.0 Boric anhydride 2.8

8. A substantially non-caking powdered material capable, when dissolved, of constituting an acid hardening fixing bath comprising Grams Anhydrous sodium thiosulfate 300 Sodium bisulfite 12.5 Potassium alum 15.0 Sodium citrate 18.0 Boric anhydride I 2.8

9. A substantially non-caking powderedmaterial capable, when dissolved, of constituting an acid hardening fixing bath comprising ,Grams Anhydrous sodium thiosulfate j 300 Sodium bisulfite 12.5 Potassium alum 15.0 Sodium tartrate 18.0 Boric anhydride 2.8

EDWIN S. WIITALA. .DONALD J. KRIDEL.

No references cited. 

1. A NON-CAKING ACID FIXING POWDER COMPOSITION CONTAINING SODIUM THIOSULFATE, AN ALKALI SULFITE, A HARDENING AGENT, BORIC ANHYDRIDE, AND A SALT OF A SOLID ORGANIC ACID SELECTED FROM THE GROUP CONSISTING OF ACETIC, CITRIC AND TARTARIC ACIDS. 